Regarding potassium hydroxide from wood ash, yes it is just as nasty as the commercially manufactured kind, if not more so (unknown other chemicals), but I think relatively low impact in its production. I have wood ash from the fire. I can either put it straight on the compost heap or pass water through it to extract potassium hydroxide first, then put it on the compost heap. If anything, the nasties ending up in my local environment are less because I've used some of them to make soap. Or possibly, the plant nutrients are less because I've used some of them to make soap. I'm not quite sure how this pans out.
I suspect that on an industrial level, no-one would be allowed to dump ash on the garden the way I'm proposing to do, but that's not part of the soap making - I've already decided to burn wood in my house, so I have the ash to dispose of. It could be worse - I could be burning coal as well
I'm not trying to argue against Gregorach's main point. I completely agree that just because something's the 'traditional' or the 'natural' way of doing something, doesn't necessarily mean it's greener.